feat(sdk): add payment workflow utilities

[Busiii-adetiba]

Summary:

• Add stream health probe with stall detection and auto-reset hooks.
• Add finality checker and receipt finality attachment helper.
• Add multisig approval workflow sequencer.
• Add operation chunker with idempotent sequential submission reporting.

Closes #536
Closes #537
Closes #538
Closes #539

Validation:

• npm test
• npx vitest run test/finalityChecker.test.ts test/approvalWorkflowSequencer.test.ts test/operationChunker.test.ts test/streamHealthProbe.test.ts
• npx tsc --noEmit --target ES2020 --module ESNext --moduleResolution bundler --strict --noUncheckedIndexedAccess --skipLibCheck src/finalityChecker.ts src/approvalWorkflowSequencer.ts src/operationChunker.ts src/streamHealthProbe.ts src/events.ts src/cursorTracker.ts src/receipt.ts

Note: npm run lint and npm run build still fail on pre-existing repository TypeScript/declaration issues in src/client.ts and related files outside this PR scope.

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